Using two or more separate UV maps and textures on the same material and model
First you will have to unfold your entire mesh and separate one area for the head and one for the body. There can be no overlapping meshes.

Now save the 'UV layout' to do the texturing.

What I did was like that, half I used for the head, and half for the body. The rest is transparent not to overwrite one image in the other at the time of placing in the blender.
Head

Body

Now just put them in the blender and that's it.